A swash plate type compressor includes a swash plate mounted directly to a rotary shaft or indirectly to the rotary shaft through a coupling member so as to be oblique to or perpendicular to the rotary shaft in a housing in which a refrigerant exists, the swash plate being in sliding contact with shoes such that the rotary motion of the swash plate is converted to reciprocating motion of pistons through the shoes, thereby compressing and expanding the refrigerant. There are two types of such swash plate type compressors, one including two-head pistons and adapted to compress and expand the refrigerant on both sides of the pistons, and one including single-head pistons and adapted to compress and expand the refrigerant on one side only of the pistons. The shoes of some swash plate type compressors slide only on one side of the swash plate, while the shoes of other swash plate type compressors slide on both sides of the swash plate.
In these swash plate type compressors, during the initial stage of operation, the swash plate and the shoes, which are both made of metal, may be brought into sliding contact with each other before lubricating oil reaches into the housing, in which the refrigerant exists. This could cause a dry lubricating state in which the sliding parts slide against each other with no lubricating oil therebetween, which in turn could cause seizure. With more recent swash plate type compressors in which carbon dioxide gas is used as a refrigerant, since the pressure in the compressor reaches as high as 10 MPa, the sliding pressure between the swash plate and the shoes increases even higher, thus further increasing the possibility of seizure at the sliding parts of the swash plate.
In order to prevent such seizure, it has been proposed to form a metal spray coating layer on each of the sliding surfaces of the metal swash plate on which the shoes slide by metal spraying of a copper type or aluminum type metallic material, and to form on the metal spray coating layer, lead type plating, tin type plating, lead-tin type plating, polytetrafluoroethylene (PTFE) type coating, molybdenum disulfide coating, or a coating of a mixture of molybdenum disulfide and graphite (see e.g. JP Patent Publication 8-199327A). It has also been proposed to form a lubricating film comprising a solid lubricant such as molybdenum disulfide or polytetrafluoroethylene, a transfer amount adjusting agent such as earthy graphite, and a binder such as polyamideimide on the sliding surfaces of the swash plate through a metal spray coating layer of aluminum (see e.g. JP Patent Publication 2002-089437A).
The purpose of forming a metal spray coating layer of a copper type or an aluminum type between the metal substrate of the swash plate and the resin lubricating coating film is to prevent peeling of the resin lubricating coating film even if the resin lubricating coating film seizes. By using a soft metal of a copper type or an aluminum type, it is possible to prevent the shoes and the metal substrate from directly coming into sliding contact with each other, thus preventing a fatal seizure accident, even if the resin lubricating coating film becomes worn.
But since the metal spray coating layer is costly and also tends to lower the flatness of the swash plate, it is also being considered to omit such a metal spray layer. For example, in order to prevent seizure, it is proposed to form sliding layers on the swash plate which comprise a solid lubricant containing polytetrafluoroethylene and hardened with polyamideimide resin, which is a thermosetting resin, and to form, on the shoes which are brought into sliding contact with the swash plate, nickel type plating, thereby further improving lubricity between the swash plate and the shoes (JP Patent Publication 2003-138287A).
If a coating film which is wear-resistant and of high strength is formed on the swash plate, such a coating film is poor in conformability, which increases sliding resistance, which tends to increase the possibility of peeling of the coating film. Thus, in order to improve the friction properties in fluid lubrication, boundary lubrication and dry lubrication states, it is proposed to a plurality of concentric circumferential grooves and ribs between the adjacent grooves (PCT Publication WO2002/075172).
As stated above, it is costly to form a metal spray coating layer of a copper type or aluminum type material on the surface of the substrate as an intermediate layer. Also, such a metal spray coating layer tends to lower the flatness of the swash plate.